1. Field of the Invention
The present invention relates to apparatus and methods for hearing aid performance measurement, fitting, and initialization.
2. Description of the Prior Art
In general, hearing aid performance measurements, whether on the production line or in the individual wearer's ear, have used an external test system that generates the test signal and analyzes the response. For example, an audiogram is a major tool used in fitting a hearing aid. An audiogram is a measurement of hearing loss, typically plotted as loss in dB as a function of frequency. Measuring an audiogram typically involves playing a set of tones through headphones while adjusting the level and frequency of the tones, and having the patient indicate whether each tone can be heard or is inaudible. Computer systems for measuring audiograms are commercially available. U.S. Pat. No. 4,548,082 to Englebretson et al describes one method for measuring an audiogram.
The measurement of the frequency response of a hearing aid in the ear, for example, typically requires the use of external signal generating and measurement equipment (Egolf, D. P., Tree, D. R., and Feth, L. L., 1978, “Mathematical predictions of electroacoustic frequency response of in situ hearing aids”, J. Acoust. Soc. Am., Vol. 63, pp 264–271; Bade, P. F., Engebretson, A. M., Heidbreder, A. F., and Niemoeller, A. F., 1984, “Use of personal computer to model the electroacoustics of hearing aids”, J. Acoust. Soc. Am., Vol. 75, pp 617–620; Sanborn, P-E, 1998, “Predicting hearing aid response in real ears”, J. Acoust. Soc. Am., Vol. 103, pp 3407–3417). Measurements of the feedback path from the receiver back to the hearing aid microphone also have required the use of external equipment (Egolf, D. P., Howell, H. C., Weaver, K. A., and Barker, S., 1985, “The hearing aid feedback path: Mathematical simulations and experimental verification”, J. Acoust. Soc. Am., Vol. 78, pp 1578–1587), as does the determination of the maximum output signal level (Revit, L. J., 1994, “Using coupler tests in the fitting of hearing aids”, in Strategies for Selecting and Verifying Hearing Aid Fittings, ed. by M. Valente, New York: Thieme Medical Publishers).
A conventional digital hearing aid is shown in FIG. 1A (prior art). Input sound signal 152 is converted into an audio signal by microphone 154. Hearing aid processor 156 is a digital signal processor (analog to digital conversion at the input and digital to analog conversion at the output are omitted for clarity). The processed audio signal is amplified by amplifier 158 and converted back into a sound signal 162 by receiver 160. Conventional digital hearing aids like hearing aid 110 use digital signal processing for the run time system, but still rely on conventional measurement equipment for measuring the hearing aid response and setting the processing parameters. Most digital hearing aids do not contain a programmable DSP circuit, but instead use a dedicated processor that can only perform the run time processing operations (Schweitzer, C., “Development of digital hearing aids”, Trends in Amplification, Vol 2, pp 41–77). These hearing aids are therefore incapable of performing any measurements, calibration, or parameter initialization.
An example of a conventional hearing aid test system 101 is illustrated in FIG. 1B (prior art). The hearing aid 110 to be evaluated is placed in a test box 102. The input to hearing aid 110 is an acoustic test signal 109 from loudspeaker 108, also contained in test box 102. Hearing aid 110 is configured to perform the desired signal processing function, such as linear gain or multiband compression. The hearing aid output is an acoustic signal that is then piped to acoustic coupler 114 via a piece of tubing 113. The acoustic coupler consists of a microphone 118 placed at the end of a cavity 116. An external computer 104 controls the generation of test signal 109 and acquires and processes the microphone response 120. Display 116 displays test results. A commercial hearing aid test system that conforms to this basic design is the Fonix 6500, manufactured by Frye Electronics, Inc, Tigard, Oreg. 97223.
For independently performing measurements, the digital hearing aid must be able to accept a program for generating a test signal and recording the response as well as accept the program for the run time processing. A need remains in the art for apparatus and methods for integrated hearing aid performance measurement, fitting, and initialization.